1. Field of the Invention
The present invention relates to a positioning method and system, and particularly to a wireless communication positioning method and system aided by geomagnetic information.
2. Description of the Related Art
Most conventional positioning techniques determine the location of a mobile station according to signals transmitted from the mobile station to a plurality of base stations. Some popular positioning techniques are ‘angle of arrival (AOA)’, ‘time of arrival (TOA)’, and ‘time difference of arrival (TDOA)’ positioning methods. FIG. 1 illustrates the AOA positioning method for positioning a mobile station at point A. Angles α1 and α2 are calculated once base stations S1 and S2 receive signals from the mobile station. Point A is located at the position, which forms an angle α1 with base station S1 and an angle α2 with base station S2. FIG. 2 illustrates the TOA positioning method for positioning a mobile station at point A. Distances between the mobile station and each base station S1, S2, and S3 can be estimated by the time spent in transmission. As shown in FIG. 2, three circles can be drawn using the positions of base stations S1, S2, and S3 as centers, and distances between each base station and the mobile station as radii. Point A is the intersection of these three circles. FIG. 3 illustrates the TDOA method for positioning a mobile station at point A. Point A is found by computing two functions, and point A is located at the intersection of the two curves representing these two functions. The first function is derived from the transmission time difference between base stations S1 and S2, and the second function is derived from the transmission time difference between base stations S2 and S3. Another popular positioning method is estimating the distance between a base station and a mobile station according to the strength of a received signal. Similarly, the location of the mobile station can be estimated by computing the distance information from three different base stations. A limitation of the conventional positioning methods discussed above is that information such as angle, time, or signal strength must be collected from at least two base stations, so that a single location can be determined.
The AOA positioning method is not suitable for urban environments with high building density as the measured angles are greatly affected thereby. In order to determine a single location, both the TOA positioning method and TDOA positioning method require at least two base stations to estimate the transmission time. The positioning method based on signal strength also require three base stations to measure signal strength, and estimating the distance according to signal strength usually generates excessive errors.
The present invention provides a positioning method requiring only one base station aided by geometric measurements. The positioning method of the present invention can be easily implemented in the 3G telecommunication system to provide positioning services such as electronic mapping.